Dynamics of Propane in Nanoporous Silica Aerogel: A Quasielastic Neutron Scattering Study

Molecular motion of hydrocarbons under confinement exhibits several peculiarities and has important implications in industries like gas recovery. A quasielastic neutron scattering (QENS) study of the dynamics of propane in nanoporous silica aerogel was carried out to quantify its molecular mobility. The dynamical properties of propane were studied as a function of temperature, pressure and presence of CO₂. The effects of pressure, i.e., fluid density and composition, are found to be more pronounced than the effects of temperature. At low pressures of propane, many propane molecules are adsorbed onto the pore surfaces and are thus immobile. As the pressure of propane loading is increased, more molecules become available to take part in the diffusional dynamics and thus enhance the diffusivity. At low pressure the propane molecules take part in a continuous diffusion, while at higher pressures, the diffusion of propane molecules within the aerogel occurs via the mechanism of jumps. Presence of CO₂ enhances the jump rate of propane molecules, thereby increasing the diffusion coefficient. This study aims to aid in understanding the complex processes involved in hydrocarbon migration in porous quartz-rich rocks and enhanced hydrocarbon recovery.